<template>
  <div class="pagination">
  <!-- 上 -->
    <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)" :class="{active:pageNo ==1}">上一页</button>
    <button v-if="startNumAndEndNum.start> 1" @click="$emit('getPageNo',1) ">1</button>
    <button v-if="startNumAndEndNum.start > 2">···</button>
   
   <!-- 中间部分 -->
    <button v-for="(page,index) in startNumAndEndNum.end" :key="index" 
    v-show="page > startNumAndEndNum.start" @click="$emit('getPageNo',page)"
    :class="{active:pageNo ==page}"
    >{{page}}</button>
    
    <!-- 下 -->
    <button v-if="startNumAndEndNum.end > totalPage -1">···</button>
    <button v-if="startNumAndEndNum.end < totalPage" :class="{active:pageNo ==totalPage}">{{totalPage}}</button>
    <button :disabled="pageNo==totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}}条</button>
  </div>
</template>

<script>
import { Math } from 'lodash/_freeGlobal';

export default {
  name: "Pagination",
  props:['pageNo','pageSize','total','continues'],
  computed:{
    // 计算出总共多少页
     totalPage(){
        return Math.ceil(this.total / this.pageSize);
    },
    // 计算出连续的页码的起始数字与结束数字
    startNumAndEndNum(){
        const {pageNo,continues,totalPage} = this;
        // 先定义两个变量储存起始数字与结束数字
        let start= 0, end =0;
        // 连续页码不够 5
        if(continues > totalPage){
            start = 1;
            end = totalPage;
        }else{
            // 正常现象 连续代码大于5 
            // 起始数字
            start = pageNo - Math.floor(continues/2) ;
            // 结束数字
            end = pageNo + Math.floor(continues/2)
            // 把出现不正常现象 start数字出现0 || 负数  纠正
            if(start < 1){
                start = 1;
                end = continues;
            }else if( end > totalPage){
                // 把出现不正常的现象 end数字大于总页码
                end = totalPage;
                start = totalPage - continues+1;
            }
            
        }
        return {start,end}
    }
  }
};
</script>

<style lang="less" scoped>
.pagination {
    text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;

    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>
